Southern California Coastal Response to the 2015-2016 El Nino

Widespread erosion associated with energetic waves of the strong 2015-2016 El Nino on the U.S. West Coast has been reported widely. However, Southern California was often sheltered from the northerly approach direction of the offshore waves. The few large swells that reached Southern California were not synchronous with the highest tides. Although west coast-wide tidal anomalies were relatively large in 2015-2016, in Southern California, total water levels (sum of tides, anomalies, and wave superelevation) were lower than during the 1997-1998 Nino, and comparable to the 2009-2010 Nino. Airborne lidar surveys spanning 300km of Southern California coast show the beach response varied from considerable erosion to accretion. On average, the shoreline moved landward 10m, similar to the 2009-2010 El Nino. Some San Diego county beaches were narrower in the 1997-1998 El Nino than in 2015-2016, consistent with the higher erosion potential in 1997-1998. Beach retreat exceeded 80m at a few locations. However, 27% of the shoreline accreted, often in pocket beaches, or near jetties. While adjacent beaches eroded, estuary mouths accreted slightly, and several estuaries remained or became closed during the study period. Only 12% of cliffs eroded (mostly at the base), and the average cliff face retreat was markedly less than historical values. Only two cliff-top areas retreated significantly. Although some areas experienced significant change, the potential for coastal erosion and damage in Southern California was reduced compared to the 1997-1998 El Nino, because of low rainfall, a northerly swell approach, and relatively limited total high-water levels.